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Coenzyme Q. Computer graphic of the molecule of coenzyme Q or ubiquinone. The green spheres represent carbon, the red spheres are oxygen and the white spheres are hydrogen. Ubiquinones are present in mitochondria, the "power stations" of cells. They form part of the cells' electron transfer chain, a process by which oxygen atoms are given electrons (reduced). This releases energy to produce adenosine triphosphate (ATP). ATP acts like a battery, storing energy in its chemical bonds. Coenzymes are low-weight, non- protein organic molecules that are necessary for the activity of enzymes.